ESSENTIALS OF DIAGNOSIS
Exposure to bird and bat droppings; common along river valleys (especially the Ohio River and the Mississippi River valleys).
Most patients asymptomatic; respiratory illness most frequent clinical problem.
Disseminated disease common in AIDS or other immunosuppressed states; poor prognosis.
Blood and bone marrow cultures and urine polysaccharide antigen are useful in diagnosis of disseminated disease.
Histoplasmosis is caused by Histoplasma capsulatum, a dimorphic fungus that has been isolated from soil contaminated with bird or bat droppings in endemic areas (central and eastern United States, eastern Canada, Mexico, Central America, South America, Africa, and Southeast Asia). Cases of histoplasmosis are increasingly being identified outside of the recognized endemic regions. Infection presumably takes place by inhalation of conidia. These convert into small budding cells that are engulfed by phagocytes in the lungs. The organism proliferates and undergoes lymphohematogenous spread to other organs.
Most cases of histoplasmosis are asymptomatic or mild and thus go unrecognized. Past infection is recognized by pulmonary and splenic calcification noted on incidental radiographs. Symptomatic infection may present with mild influenza-like illness, often lasting 1–4 days. Moderately severe infections are frequently diagnosed as atypical pneumonia. These patients have fever, cough, and mild central chest pain lasting 5–15 days.
Clinically evident infections occur in several forms: (1) Acute pulmonary histoplasmosis frequently occurs in epidemics, often when soil containing infected bird or bat droppings is disturbed. Clinical manifestations can vary from a mild influenza-like illness to severe pneumonia. The illness may last from 1 week to 6 months but is almost never fatal. (2) Progressive disseminated histoplasmosis most frequently occurs in patients with underlying HIV infection (with CD4 cell counts usually less than 100 cells/mcL) or other conditions of impaired cellular immunity. Disseminated histoplasmosis has also been reported in patients from endemic areas taking tumor necrosis factor (TNF)-alpha inhibitors. It is characterized by fever and multiple organ system involvement. Chest radiographs may show a miliary pattern. Presentation may be fulminant, simulating septic shock, with death ensuing rapidly unless treatment is provided. Symptoms usually consist of fever, dyspnea, cough, loss of weight, and prostration. Ulcers of the mucous membranes of the oropharynx may be present. The liver and spleen are nearly always enlarged, and all the organs of the body are involved, particularly the adrenal glands; this results in adrenal insufficiency in about 50% of patients. Gastrointestinal involvement may mimic inflammatory bowel disease. Central nervous system (CNS) invasion occurs in 5–10% of individuals with disseminated disease. (3) Chronic pulmonary histoplasmosis is usually seen in older patients who have underlying chronic lung disease. Chest radiographs show various lesions including complex apical cavities, infiltrates, and nodules. (4) Complications of pulmonary histoplasmosis include granulomatous mediastinitis characterized by persistently enlarged mediastinal lymph nodes and fibrosing mediastinitis in which an excessive fibrotic response to Histoplasma infection results in ...